ABSTRACT
The oral route of administration is considered the easiest, most convenient and widely used drug delivery route. One of the hardest challenges facing oral drug delivery systems (DDS) is the erratic absorption of drugs through the gastrointestinal tract (GIT). The conventional oral dosage forms usually suffer from low bioavailability especially in case of drugs with narrow absorption window (NAW). The oral controlled release dosage forms could overcome the previous limitation by providing predicted and calculated drug release, resulting in improvement of the efficacy of drugs. One of the most promising types of oral controlled release dosage forms for this purpose is the gastro retentive drug delivery system (GRDDS), which was found to improve the gastric retention of the dosage form and maximize the absorption and bioavailability of the drugs with NAW. In this review, we summarize the different GRDDS techniques used for improving drug absorption, their methods of preparation, and their mechanisms of action.